1. Field of the Invention
This invention relates to the field of video matte or background generators, and in particular to a color matte synthesizer that calculates from user control inputs respecting luminance, saturation and hue, a plurality of amplitude samples that fully define one period of chroma cycle of a video signal corresponding to the user's selections, these amplitude samples then being sequentially read out in time division multiplex manner and superimposed with synchronizing information, to produce the desired video matte in a signal that can be displayed on a standard color television monitor.
2. Prior Art
Matte generators have been in use for some time in the video production industry. The user generally selects, using potentiometers, a desired luminance, saturation and hue for the matte display. The conventional matte generator uses algorithms or electronic circuitry to produce analog signals relating to the primary video colors, namely red (R), green (G) and blue (B). The R, G and B signals are then electronically encoded to form a composite baseband video signal if the matte is to be displayed on a standard television monitor.
U.S. Pat. No. 4,636,839--Cole et al discloses a matte generator that converts luminance, saturation and hue to RGB levels in a microprocessor. The microprocessor computes difference values R-Y, B-Y and also luminance (Y), along with an address, this computation being effected once for each video field. The apparatus is complex in that multiple conversions are required, namely from luminance/saturation/hue to RGB to R-Y/B-Y/Y. The disclosure does not teach a method or apparatus for converting the calculated values (once per field) to a signal which might be displayed on a standard video monitor, the addition of which would further increase the complexity of the apparatus.
U.S. Pat. No. 4,758,880--McFetridge discloses another complex system, in this case generating a video matte signal which must be decoded to produce a baseband video signal for displaying the matte. The system relies on two subcarrier oscillators in quadrature. A digital to analog converter is used to produce relatively steady state DC values (during the vertical interval time), which are used to control in-phase and quadrature modulators. Like Cole et al, McFetridge goes through an encoding stage before attempting to generate composite baseband video. The present invention, on the other hand, uses a microprocessor to proceed directly from control inputs to samples defining the luminance, saturation and hue information, which samples are read out sequentially and repeatedly during the viewable portion of the video, then added to synchronization signals to reproduce a composite video matte signal in a direct and uncomplicated manner.
Additional devices are known for processing an existing video signal to correct or adjust luminance, saturation and/or hue. These are not matte synthesizers. Reference can be made, for example to U.S. Pat. No. 4,642,682--Orsburn et al; U.S. Pat. No. 4,542,402--Ader; and, U.S. Pat. No. 4,809,059--Flamm et al. The systems disclosed do not synthesize chroma signals and are complicated. The typical output is not composite video, but rather is RGB, R-Y/G-Y/Y or the like, to be further processed in a television receiver or the like.
U.S. Pat. No. 4,442,428--Dean et al discloses a limited capability matte generator. The available colors are not variable, a limited subset of colors being selectable by the user. Additional disclosures which do not concern matte synthesizers but may be of interest in the field of video signal processing can be found in U.S. Pat. No. 4,404,583--Tatami; U.S. Pat. No. 4,176,373--Dillone et al; and U.S. Pat. No. 4,327,373--Giomi.
Unlike the prior art, the present invention synthesizes a video baseband output directly from selections at continuously adjustable user inputs inputs for luminance, saturation and hue. The inputs and outputs are high in resolution, yet the device is versatile and uncomplicated. These features are achieved by digitizing user control inputs for the three variables, calculating the level of the corresponding baseband video signal at a plurality of sequential samples in the period of the subcarrier, and reproducing the baseband video output by repetitively reading out the samples, thereby obtaining the required level and phase relationships needed.